With the rapid development of computer, electronic and communication technology, various wireless communication services using a wireless network have been provided. The most basic wireless communication service is a wireless voice communication service for providing voice communication to mobile communication terminal users in wireless manner, which has a characteristic of providing the service to the users regardless of time and place. Further, the wireless communication service supplements a voice communication service with a text message service. Recently, a wireless Internet service has emerged, which provides an Internet communication service to mobile communication terminal users through a wireless network.
Accordingly, subscribers of a mobile communication service can not only communicate with partners by using a wireless communication service regardless of time and place while freely moving here and there, but also receive various information, such as news, weather, sports, stocks, exchange rates and traffic information, in the form of texts, voice, images, etc.
With the development of mobile communication technology as described above, services provided by a Code Division Multiple Access (Hereinafter, referred to as CDMA) mobile communication system have been developed from voice services to multimedia communication services for transmitting data such as circuit and packet data.
Recently, with the development of information communication, an International Mobile Telecommunication (Hereinafter, referred to as IMT)-2000, e.g., a CDMA 2000 1×, 3×, EV-DO or a Wideband CDMA (WCDMA), has been commercialized, which is the 3rd mobile communication system and has been established as a standard by an International Telecommunication Union Recommendation (ITU-R). Further, a wireless Internet service has been provided at a transmission speed of 307.2 Kbps at maximum far faster than 14.4 Kbps or 56 Kbps, which is a data transmission speed supported by an Interim Standard (Hereinafter, referred to as IS)-95A network or an IS-95B network, by means of an IS-95C network evolved from the existing IS-95A network and IS-95B network. In particular, an IMT-2000 service is used, so that the quality of an existing voice and Wireless Application Protocol (WAP) service can be improved and various multimedia services, e.g., Audio On Demand (AOD), Video On Demand (VOD), etc., can be provided at higher speed.
Recently, an RBT service or a so-called coloring RBT service has been highlighted, in which various sounds customized by the user of a call-receiving mobile communication terminal are outputted to a mobile communication terminal or a general telephone of a calling party as RBTs. This RBT service includes a concept for RBTs designated by a called party to be provided to a calling party. That is, the RBT service is a service in which the newest Korean songs, pop songs, a recorded voice, bird or water sounds, etc., can be used as RBTs instead of existing mechanical RBTs, e.g., “ring, ring” sound, occurring during ordinary communication.
The RBT service as described above has been provided, so that a partner can listen to sounds of a sound source customized by a called party instead of uniform and mechanical RBTs. Therefore, the partner can obtain auditory satisfaction.
Most mobile communication terminals use a voice codec having a variable rate such as an EVRC for the efficiency of voice communication and the optimization of radio channels. The EVRC is a codec for variably coding voice information according to the amount of voice information. That is, the EVRC encodes voice at a low rate during no-sound interval in which speakers do not output sound and encodes voice at high speed when the amount of information is large. It may be understood that this EVRC is an efficient codec as compared with existing codecs for always encoding voice at constant speed. The EVRC is used, so that the system capacity of a CDMA mobile communication system can increase and power consumption can also be minimized.
However, a voice codec having a variable rate such as this EVRC may deteriorate the sound quality for music, such as background sounds having nearly no-sound interval, due to a variable rate coding error. In order to overcome this problem, music service providers have made efforts to minimize the loss of sound sources due to a voice codec by extracting the sound sources and correcting the sound sources according to the EVRC. This sound source correction has depended on pre-processing considering the characteristics of the EVRC or manual operation of a sound specialist.
However, these processes may improve the quality of the music service through the EVRC nearly up to the level of the voice quality, but they have difficulty in improving the quality of the music service beyond such a level. Therefore, most high quality music services currently being provided separately use high quality multimedia codecs and provide music through data channels instead of voice channels. Herein, most of these commercialized multimedia service codecs have required transmission speeds over 16 K. In order to satisfy this transmission speed, a download service or a realtime multimedia service has been provided through data communication channels.
Accordingly, when a music service using this multimedia codec is applied to an RBT service, the quality of sound may be improved. However, a problem with the data rate required for multimedia voice transmission and the unavoidable use of voice channels instead of data channels still exists. Herein, it is theoretically possible that the data rate problem can be solved by lowering the data rate under 8 K through revision of encoding and decoding algorithms of the multimedia codec. However, in order to apply a multimedia codec for which the average rate has changed less than 8 K to voice channels through which an RBT service is currently provided, a partial modification of a mobile communication system is unavoidable.